When time travel is part of a sci-fi thriller or action-adventure film, we usually get caught up in how it all works and excitement of a journey that defies our current scientific capabilities. “Safety Not Guaranteed” takes the indie approach, exploring the more grounded aspects of time travel (as oxymoronic as it sounds), or in other words, how time travel even as just a theory can be a powerful notion.

The film uses an actual, non-fiction personal ad in which a man seeks to find someone to go back in time with as the launch point for this journey. Jeff (Jake Johnson), a staff writer at a Seattle magazine, pitches the idea of finding and talking to this guy as a story to the editor and she approves it. He takes two interns, Darius (Aubrey Plaza) and Arnau (Karan Soni), with him on the assignment, and their road trip proves to be life-changing.

Darius is the main character for all intents and purposes, though Derek Connolly’s script provides ample development for all three characters. Each has some kind of personal hurdle to clear and the trip provides them with that opportunity.

For Darius, her daring, nothing-to-lose attitude allows her to scope out and get close to Kenneth (Mark Duplass), the man who claims to be time traveling. She wins his trust, though she doesn’t do so in a manipulative way; she rather genuinely connects with him, not presenting herself in a completely false manner. Her past has in a sense rendered her emotionally hollow and she seeks something, anything different really, to fill it. Together, she and Kenneth go through his training regimen and prepare for their journey back in time.

The overall comic tone of “Safety Not Guaranteed” is deadpan. It’s character-driven both in humor and story, with Duplass and Plaza practically epitomizing the general vibe of the script and the film. Director Colin Trevorrow must simply find ways to allow these quirky personalities to shine in the sincerest and most human way possible. In your average comedy, Darius is the cold bitch, Jeff the former player turned desperate single guy, Arnau the nerdy Indian virgin and Kenneth the wack-job, but these characters become so much more in this film. They are precious in all their flaws (and stereotypes) and we take a definite liking to them in spite of it.

Appropriately, their problems are all more or less riffs on things that involve time. Darius lost her mom at a young age, and when she tells Kenneth that’s her reason for going back in time, we know that she’s being rather truthful. Kenneth lost a girlfriend, so love motivates him. Love also motivates Jeff, who it turns out only pitched the story so he could find a girl he had an incredible fling with one summer but let get away. As for Arnau, he needs to start making the most of his life, to take risks and find his confidence. So the notion of time travel, the mere possibility of it, in fact, means something to each of them.

Keeping us engaged is the mystery of whether or not Kenneth can actually travel through time or is totally crazy. He breaks into all kinds of labs and research facilities to get the things he needs, as it turns out, and the answer comes down to the wire. Given the grounded nature of the story in all other capacities, you eventually come to realize that it probably doesn’t matter whether he can or can’t. Still, this helps command our attention.

Little ends up being groundbreaking about what “Safety Not Guaranteed” does as an independent comedy, but the way it blends this question of science fiction with incredibly honest affairs of the heart makes it a real charmer, as does the way the cast fits so effortlessly into the film’s style and mission.